Many conventional heat exchangers of the type where ambient air is utilized as one heat transfer fluid include opposed headers interconnected by tubes. In the usual case, fins extend between the tubes. Air is caused to flow between the tubes and through the fins in a direction generally transverse thereto.
One measure of the ability of such a heat exchanger to exchange a given quantity of heat over a unit of time is the effective frontal area of the heat exchanger. This area is equal to the area of the entire heat exchanger normal to the path of airflow less that part of such area occupied by the headers and/or tanks conventionally associated therewith. Typically, this area is the frontal area of the so-called "core" which basically is the fin and tube assembly of the heat exchanger.
In some applications, size constraints may not be present and in such a case, the core may be built of sufficient size so as to provide the desired frontal area without regard for the additional volume occupied by the tanks and/or headers. In others, however, only a given area is available to receive the entire heat exchanger. In these cases, the core size must be maximized to maximize heat transfer ability. At the same time, because of size constraints, the volume of the tanks and/or headers may limit the size of the core and thus limit heat exchange ability.
One typical application in which size constraints are present is in vehicles. Because of increasing concern over the last decade or so for energy efficiency, vehicle manufacturers have sought to produce more aerodynamically designed vehicles with lower drag coefficients and this has produced constraints on the frontal area of the vehicles whereat heat exchangers such as radiators, condensers, evaporators, oil coolers and the like may be located. In addition, vehicle manufacturers have sought to reduce the weight of the various components utilized in the vehicle as a means of improving fuel utilization and heat exchangers have not been immune from the search for ways to reduce weight.
More recently, there has been increasing concern about the escape of chlorofluorocarbons or so-called CFCs or other potentially harmful cases into the atmosphere. One source of escaping CFCs is leaking refrigerant from an air-condition system. Clearly, if the refrigerant charge volume of a vapor compression refrigeration or air conditioning system can be reduced, then the consequences of a leak in any given system in terms of the amount of CFCs released to the atmosphere is lessened because of the lesser volume of CFCs in such a system.
Still another concern unique to air-conditioning or refrigeration systems is the efficiency of the evaporator utilized in a typical vapor compression refrigeration system. All too frequently, the temperature of a fluid stream passing through an evaporator varies widely from one location to another across the rear face of the evaporator. This is indicative of poor efficiency in the heat transfer operation which desirably would result in substantial uniformity of the temperature of the exiting airstream from one location on the evaporator to another. Such uniformity is indicative of a uniform temperature differential and good heat transfer efficiency.
It has long been postulated that these temperature differentials result from poor distribution of the refrigerant within the evaporator. Those parts of the evaporator receiving more refrigerant will run colder than those receiving less. Thus, elaborate distributor schemes have been devised in many attempts to achieve uniform distribution of refrigerant through the many passages of the evaporator. While such distributors work well in a number of instances, their complexity results in an expensive construction which in itself is not conducive to their use. The present invention is directed to solving one or more of the above as well as other problems.